GitLab

Sometimes [ToolbarMediator updateShareMenuForWebState:]
is passed a null WebState, so do nothing if that is the case.

Bug: 
Change-Id: Id083687df59199489a80ca21a9182113e2ad62ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354710
Auto-Submit: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797763}